Strange moment behavior

Grasshopper Karamba3D
1

Hi,

Although all beam elements are connected according to Karamba 1.3.3, supposedly moment stiff and not hinged, I get this strange moment behavior. From A to B I expected a continuous-beam-over-support effect. The moment curve should be more like a wave over the supports. The loads on meshes are equally distributed. Any clue?

Strange moment
Strange moment711×350 33.7 KB
Continuous bamboo culms
Thanks in advance for any ideas,
Ingemar

2

Hi @ingemar,
it seems like you need to increase the number of results per beam. Reduce ‘Length/Segment [m]’ in the ‘ModelView’-component in submenu ‘Render Settings’ (see here) from ‘1’ to a number which makes the moment diagrams appear more smooth.
Also check whether the resolution of the mesh used for the Mesh-Loads is sufficiently high (i.e. the mesh faces are small enough).
– Clemens

3

Hi Clemens,
Thanks for reply.
1 However, Reducing Length/Segment does not change much, at least not the sharp moment profile. Continuous beam over support should make a wave like moment graph, right?
2 Dividing meshes to get smaller faces (and higher resolution) I cannot find in the Karamba toolbox. Should I do that in Rhino?
3 My definition may be corrupt altogether; when I change the Beam Cross section measure I don’t see any change in the Assemble/Mass to reflect this in kg. I attach the -gh and -3dm files for detecting this.
4 I also would like to switch of the meshes in the Model View so as to better observe the shell behavior under exaggerated stress.
Greetings,
Ingemar

Canopy_5apr.gh (84.9 KB) CANOPY_5apr.3dm (122.0 KB)

4

Hi @ingemar,

first of all, the definition is unfortunately very hard to debug, because it is not structured very well. You also have two shell elements, and you have not used the Cross Section component to define a cross sections yet.

Another issue is that your mesh is not connected to your line members. You can use the MeshBreps component to allow for connections by using mesh vertices: 3.8.1: Mesh Breps - Karamba3D 1.3.3

The bending moment is correct and should not be continuous, you can see that torsional moment in the members which accounts for the jumps in the bending moment.

best,
Matthew